In the class of hearing aids generally referred to as implantable hearing instruments, some or all of various hearing augmentation componentry is positioned subcutaneously on or within a patient's skull, typically at locations proximate the mastoid process. In this regard, implantable hearing instruments may be generally divided into two sub-classes, namely semi-implantable and fully implantable. In a semi-implantable hearing instrument, components such as a microphone, signal processor, and transmitter may be externally located to receive, process, and inductively transmit an audio signal to implanted components, e.g. an implantable receiver and transducer. In a fully implantable hearing instrument, all of the components, e.g. the microphone, signal processor, and transducer, may be located subcutaneously. In either arrangement, the implantable transducer is utilized to stimulate a component of the patient's auditory system, e.g. a middle ear component or inner ear.
By way of example, one type of implantable transducer includes an electromechanical transducer having a magnetic coil that drives a vibratory actuator. The actuator is positioned to interface with and stimulate the ossicular chain of the patient via physical engagement. (See, e.g. U.S. Pat. No. 5,702,342). In another approach, implanted excitation coils may be employed to electromagnetically stimulate magnets affixed within the middle ear. (See, e.g. U.S. Pat. No. 5,624,376). In each of these approaches, a changing magnetic field is employed to induce vibration of a middle ear component, e.g. one or more bones of the ossicular chain, thereby stimulating the cochlea through its natural input, i.e. the oval window. In other approaches, an implantable transducer is located within the inner ear or in direct contact with the round window of the inner ear of a patient, wherein vibrations are imparted to the cochlear fluid of the patient. For example, the implantable transducer may be defined by a microactuator that functions like a parallel plate capacitor, wherein applied voltage changes across the “plates” yields electrostatic forces that cause one of the plates to functionally flex as a diaphragm to input vibrations to the cochlear fluid of a patient. (See, e.g. U.S. Pat. No. 5,984,859). In another arrangement, a number of output-side electromechanical transducers may be disposed on or within a mechanical carrier that is positioned within the inner ear. (See e.g. U.S. Pat. No. 6,575,894).
In the case of implantable transducers designed to interface with the ossicular chain, the establishment/maintenance of a desired interface between the implantable transducer and the ossicular chain is important for proper instrument operation. For instance, stimulation of the ossicular chain through vibration relies at least in part on an intimate contact interface between the ossicular chain and transducer. Overloading or biasing of the implantable transducer relative to the ossicular chain can result in degraded performance of the biological aspect (movement of the ossicular chain), possibly causing an additional impairment of hearing, as well as degraded performance of the mechanical aspect (movement of the transducer). Further, if the implantable transducer is underloaded relative to the ossicular chain, e.g. a loose connection or no physical contact at all, vibrations may not be effectively communicated.
Similarly, in the case of implantable transducers designed to interface directly with an inner ear, the establishment/maintenance of a desired interface between the implantable transducer and inner ear is important for proper instrument operation. For example, proper contact positioning of an implantable transducer within or on the outside of the round window of the inner ear is needed for proper stimulation of the cochlear fluid.
As may be appreciated, at the time of implant proper setup of an implantable transducer may depend on the present condition of the middle ear and/or inner ear of a patient. For instance, the positioning of the transducer and the nature of the sound processing parameters may be determined based on patient-specific biological aspects such as damage or reduced mobility of the ossicular chain, etc. Over time, such aspects may change and additional pathological aspects may develop. These changes or developments, in turn, may affect the performance of the implanted transducer, e.g. such as by changing the engagement between the transducer and the ossicular chain or inner ear.